The present invention is directed to a control system for a power-operated moving object, such as a vehicle door, gate, or trunk, and more particularly to a control system that controls clutch engagement during power-operated movement of the moving object.
Systems for moving objects, such as openable vehicle body members (e.g., sliding vehicle doors, lift gates, trunks, and the like), often incorporate a clutch to allow a user to move the object/openable member manually. Vehicles, particularly larger vehicles such as sport utility vehicles and mini vans, may have systems as a sliding door or lift gate that incorporate a clutch. In these systems, the clutch is engaged only when a controller takes over movement of the openable member.
More particularly, when a controller senses the user""s manual movement of the object, the controller takes over movement of the object in a power assist function by engaging the clutch and starting the motor. Because the clutch engages when the object is moving faster than the motor, however, the speed difference between the object and the motor may cause clutch shock.
If the user wishes to move the object more quickly than the speed dictated by the controller, the controller may initiate a power release function by monitoring the speed and/or force of the object movement. More particularly, if the speed and/or force exceed a selected threshold, the controller allows the user to continue moving the object without any motor assistance.
However, because the conditions for initiating a power assist function can become true before the conditions for a power release function become true, the clutch may be engaged and the controller may take over even after the power release conditions have been met, which is not desirable for a user who wants to operate an object manually.
There is a desire for a control system that avoids clutch shock in both power assist and power release operations. There is also a desire for a control system that can easily distinguish between a power assist condition and a power release condition.
The present invention is directed to a control system and method that compares the motor speed with the object speed and engaging the clutch when the motor and object speeds are almost equal. The invention is also directed to a control system and method that can distinguish between a power assist condition and a power release condition and control clutch engagement accordingly. In one embodiment, the system controls the motor speed so that it increases at a gradual rate, ensuring that the control system can distinguish between the power assist condition and the power release condition. By waiting until the motor and the object are moving at nearly the same speed before engaging the clutch, the inventive control system avoids clutch shock and allows smooth clutch engagement. The invention also smoothes transitions between the power assist mode and the power release mode to prevent clutch shock when switching between the two modes.